Shadow mask supported by bimetallic spring comprising coplanar strips with different coefficients of expansion

ABSTRACT

A color display tube in which the shadow mask is suspended by means of resilient strips which consist of strips of metals having different coefficients of expansion, the narrow sides of which are welded together, the welding seam extending along the longitudinal axis of the strip, and the strip upon heating being bent in its plane in such a manner that the mask is moved towards the display screen.

United States Patent Inventors Gerardus Antonius Hafkenscheid;

Gerardus Wilhelmus Plukker; Jan Willem Ruis, Emmasingel, Eindhoven, Netherlands Appl No. 795,969 Filed Feb. 3, 1969 Patented Apr. 6, 1971 Priority Feb. 8, 1968 Netherlands 6801741 SHADOW MASK SUPPORTED BY BIMETALLIC SPRING COMPRISING COPLANAR STRIPS WITH DIFFERENT COEFFICIENTS OF EXPANSION [56] References Cited UNITED STATES PATENTS 3,330,980 7/1967 Schrader 313/858 3,449,61 1 6/1969 Schwartz et al. 3 l 3/92BX 3,452,234 6/1969 Lindeman 313/858 3,479,546 1 H1969 Mears 313/855 Primary Examiner-Robert Segal AttorneyFrank R. Trifari ABSTRACT: A color display tube in which the shadow mask is suspended by means of resilient strips which consist of strips of metals having different coefficients of expansion, the narrow sides of which are welded together, the welding seam extending along the longitudinal axis of the strip, and the strip upon heating being bent in its plane in such a manner that the mask is moved towards the display screen.

Patentd A ril 6, 1971 I 3,573,527

2 Sheets-Sheet 1 INVENTORS GERARDUS mmrnemrnem By GERAROMS w. PLUKKER JAN van ls Patented April 6, 1971 3,573,527

2 Sheets-Sheet 2 INVENTORS GERARDUIS A, HAFKENSC HEID BY PLUKKER iwu SIIIAIDUW MASllf SUFIPGIR'IIIEID IBY IBIIMIIE'IIAILILIIC SIPIMNG CGMIPIRIISIING CUlPlLANAR S'llttIlPS Wll'llllll DIFFERENT CUIEIFIFIICIIIEN'IS OIF EXPANSION The invention relates to a resilient suspension member for securing a color-selection electrode, particularly a shadow mask, in the glass envelope of a cathode ray tube for display ing colored television images. The invention particularly relates to such a suspension member which partly consists of a bimetal and is arranged in such a manner that the color-selection electrode upon heating acquires a component of movement in the direction towards the display screen. Such a displacement of the color-selection electrode, particularly a shadow mask, is necessary to ensure that the electron rays still strike the correct color elements of the screen even upon expansion of the color-selection electrode due to heating.

In the known embodiments, for example, of the published Netherlands Patent Application 66,l0,027 in which the bimetal parts consist of two metal layers secured on each other and having different coefficients of expansion, the flexure always occurs in a direction at right angles to the largest surface of the layers, that is to say, in the direction of the smallest moment of resistance of the bimetal part.

The bimetal part must thus always be arranged in such a manner that this flexure is transferred directly or indirectly onto the color-selection electrode along the longitudinal axis of the tube. Conversely, however, a displacement of the colorselection electrode along the axis of the tube due to a shock or impact will always be transferred onto the bimetal part in the direction of the smallest moment of resistance of said part. It has been found that the stretching limit of at least one of the metals of the bimetal part is often exceeded so that this part undergoes a permanent deformation. The result is that upon a heavy shock against the display tube or dropping from a small height the color-selection electrode may undergo a permanent displacement directed along the axis of the tube, so that the color display is greatly affected.

The mentioned drawbacks are substantially obviated if according to the invention in such a resilient suspension member consisting at least partly of a bimetal, at least the free resilient part of the suspension member consists of a strip which is formed in that the narrow sides of the two metal layers form ing the bimetal are connected together in such a manner that the connection seam extends at least through part of the length of the free part of the strip. The strip is preferably entirely formed by two strips of different metals extending along the length, the narrow sides of which are connected together. The direction of flexure upon heating thus is no longer at right angles to the largest surface of the bimetal strip but parallel to this surface, thus in the direction of the largest moment of resistance of the strip. The suspension spring itself therefore performs not only the function of suspending the color-selection electrode but also the function of one of the two components of the bimetal. This is possible because the largest surface of the layers of the bimetal consisting of different metals do not lie upon each other but are secured to each other on their sides. The resilience of the layers in the direction at right angles to their surface is therefore not adversely affected.

It has been found that the flexure in the plane of the strip is effected without torsion of the strip occurring if the two layers of the bimetal connected together on their narrow sides are formed in such a manner that the connection seam is uninterrupted and extends through part, or preferably throughout the whole free length of the resilient strip formed by these layers. and that in addition this free part of the strip lies in a flat plane and is straight as viewed on the narrow side. Since the forces occurring in the metal layers are comparatively very large, it is necessary to ensure a very satisfactory connection of the sides of the layers throughout the length, since otherwise flexure or torsion of the strip may locally occur. One layer preferably consists of invar, which has a very low thermal coefficient of expansion, the other of stainless steel which has a much higher thermal coeflicient of expansion. The connection of the strip to the color-selection electrode must also be very rigid. To this end the strip has a projecting portion which can be bent around the edge of the supporting frame: of the color-selection electrode. Two projecting tags which facilitate bending are preferably provided for this purpose.

In order that the invention may be readily carried into effect it will now be described in detail by way of example with reference to the accompanying diagrammatic drawings, in which:

FIG. l is a side view;

FIG. 2 is a plan view;

FIG. 3 is a cross section taken on the line ll-Il of FIG. I ofa resilient strip according to the invention;

FIG. 4 is a perspective elevational view of a suspension member secured to a corner of a shadow mask;

FIG. 5 is a bottom view of FIG. 4',

FIG. 6 is a view of a mask having three resilient members; while FIGS. 7, it and 9 are further embodiments according to the invention.

In FIGS. I, 2 and 3 the resilient suspension member is indicated by l, which consists of a layer 2 of stainless steel (chromium nickel steel) containing approximately 18 percent by weight of chromium and 8 percent by weight of nickel and having a thermal coefficient of expansion of approximately I70.I0, and a layer 3 of invar (64 percent by weight of Fe, 36 percent by weight of Ni) having a coefficient of expansion of approximately 0. The narrow sides of the layers 2 and 3 are welded together at 6, the welding seam extending throughout the length of the resilient strip II. The strip It is provided with an aperture 7 which fits around a projection in the wall of the envelope. The wide end which is welded to the color-selection electrode is provided with two tags 4i and 5.

As is shown in FIG. 4 the member II can be provided around a corner of the supporting frame 9 and welded in position at the areas 11, said supporting frame having a reentrant flange It) and supporting a shadow mask a. The tags 4 and 5 are bent around the edge of the frame 9 and welded to the lower side of the flange It). A very rigid connection between strip and frame is obtained in this manner.

Upon heating, the layer 2 expands to a greater extent than the layer 3 so that the hollow side of the spring of FIG. II is curved on the lower side as is shown by the broken line. Since the projection I2 (FIG. 5) has a fixed position in the envelope '13 which supports the spring and the aperture 7, the curvature of the spring will cause an upward movement of the wide end and of the frame 9 secured thereto and the mask 3 so that the mask h is moved towards the phosphor screen.

Three springs 1 arranged as shown in FIG. 6 will generally be used.

The resilient strip appears to bend in its largest plane. Since large forces occur in the welding seam of the metal layers 2 and 3, strict requirements are imposed on this welding seam. It has been found that the flexure as a result of an increased temperature is smaller in the embodiments of FIGS. 7, s and 9 than in those of FIGS. 1, 2 and 3. The latter embodiments are therefore not particularly suitable. It is necessary that the welding seam s is homogeneous and is not locally interrupted. The seam is preferably welded electronically since a very homogeneous seam without ripple can then be obtained.

The securement of the wide end of the strip 1 to the frame 9 must be very rigid, since otherwise distortion may occur at the welding areas in case of heavy shocks (drop tests). The strip ll, thus the bimetal itself, is extremely strong in this case in directions parallel to the axis of the tube. The long sides of the bimetal strip need not be straight but may alternatively be bent, so that a slightly falciform strip is obtained.

It has been found from drop tests that the permanent displacement of the mask a is approximately one-half to onethird of that which occurs in the known constructions, in which separate bimetal parts are used which are connected to a resilient strip. The quality of the welding seam ti also plays an important role in this case, since it is dependent on this scam whether the strip ll behaves as a unit or that a nonresilient shift may occur between the two layers 2 and 3.

The free part of the strip 1 must preferably lie entirely in a flat plane in order to obtain the curvation in the plane of the strip. The thickness of the layers 2 and 3 in a shadow mask having a weight of 900 gm. is, for example, 1.2 mm. It was found from drop tests that the permanent displacement of the mask 8 after a shock of 60 g. may be approximately l to 20 a. In the known constructions this displacement is from 30 to 70 p.

We claim:

l. A cathode ray tube comprising an evacuated envelope having a substantially rectangular window at one end thereof, a plurality of phosphor triads constituting a luminescent screen disposed on said window, a substantially rectangular color-selection electrode having apertures therein aligned with said phosphor triads, and at least three bimetallic springs positioned along the perimeter of said electrode for supporting said electrode with minimum transferring of impacts from said envelope to said envelope, each of said bimetallic springs comprising two flat coplanar metallic strips having different coefficients of expansion along abutting longitudinal edges in a coplanar arrangement with one end secured to said electrode and the other end connected to said envelope, said strip having the greater coefficient of expansion being nearer said display screen whereby said electrode is moved in a direction towards said screen parallel to surfaces of said strips and orthogonal to longitudinal edges of said spring upon an increase in temperature of said electrode.

2. A cathode ray tube as claimed in claim 1, wherein the strip consists of a chromium nickel steel strip having 18 percent by weight of chromium, 8 percent by weight of nickel and a strip consisting of invar.

3. A cathode ray tube as claimed in claim 1. wherein the free part of the resilient strip lies in a flat plane.

4. A cathode ray tube as claimed in claim 1, wherein the end of the member which is connected to the color-selection electrode is provided with tags which can be bent around the lower edge of a supporting frame of the color-selection electrode and can be welded thereto.

5. A color-selection electrode provided with at least three suspension members as claimed in claim 1, wherein at least one of these members is bent around a comer of the colorselection electrode and is welded thereto.

gg UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Pa cent N0. 3 573 527 Dated AQril 1 Q7] InventOflSYGERARDUS ANTONIU P AND JAN WILLEM RUIS It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 2, line 25, change "170.10 to --170.10'

Signed and sealed this 13th day of July 1971.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. WILLIAM E. SCHUYLER, JR. Attesting Officer Commissioner of Patents 

1. A cathode ray tube comprising an evacuated envelope having a substantially rectangular window at one end thereof, a plurality of phosphor triads constituting a luminescent screen disposed on said window, a substantially rectangular color-selection electrode having apertures therein aligned with said phosphor triads, and at least three bimetallic springs positioned along the perimeter of said electrode for supporting said electrode with minimum transferring of impacts from said envelope to said envelope, each of said bimetallic springs comprising two flat coplanar metallic strips having different coefficients of expansion along abutting longitudinal edges in a coplanar arrangement with one end secured to said electrode and the other end connected to said envelope, said strip having the greater coefficient of expansion being nearer said display screen whereby said electrode is moved in a direction towards said screen parallel to surfaces of said strips and orthogonal to longitudinal edges of said spring upon an increase in temperature of said electrode.
 2. A cathode ray tube as claimed in claim 1, wherein the strip consists of a chromium nickel steel strip having 18 percent by weight of chromium, 8 percent by weight of nickel and a strip consisting of invar.
 3. A cathode ray tube as claimed in claim 1, wherein the free part of the resilient strip lies in a flat plane.
 4. A cathode ray tube as claimed in claim 1, wherein the end of the member which is connected to the color-selection electrode is provided with tags which can be bent around the lower edge of a supporting frame of the color-selection electrode and can be welded thereto.
 5. A color-selection electrode provided with at least three suspension members as claimed in claim 1, wherein at least one of these members is bent around a corner of the color-selection electrode and is welded thereto. 